Many enterprises are moving towards using VoIP over their LANs and WLANs to interconnect various terminal devices for voice communications. Moreover, external voice communications with remote parties through, for example, the PSTN, may be converted to VoIP communications for routing within the enterprise communication system. A Private Branch exchange (PBX) typically acts as the interface between the PSTN and the internal enterprise communication system. The PBX provides conversion between digital circuit-switched calls and VoIP calls, and assists in routing calls to the correct terminal device. SIP signaling is commonly used to set-up, manage, and tear-down media paths for the VoIP calls.
In many enterprise communication systems, a proxy server may play a significant role in setting-up and managing calls involving terminal devices. One problem that arises in this regard is ensuring that the proxy server is included in any SIP signaling between a terminal device and other SIP entities, like the PBX.
Similar reference numerals may have been used in different figures to denote similar components.